The heart is a muscular structure with four chambers and four valves. The upper chambers, which are filling chambers, are called the left and right atria. The lower chambers, which are pumping chambers, are called the left and right ventricle.
Heart valves lie at the exit of each of the four heart chambers and maintain one-way blood flow through the heart. The four heart valves make sure that blood always flows freely in a forward direction and that there is no backward leakage.
- The tricuspid valve regulates blood flow between the right atrium and right ventricle.
- The pulmonic valve controls blood flow from the right ventricle into the pulmonary arteries, which carry blood to the lungs to pick up oxygen.
- The mitral valve lies between the left atrium and the left ventricle. It prevents blood from leaking back into the left atrium during left ventricular contraction.
- The aortic valve lies between the left ventricle and the aorta (the largest artery in the body). It opens the way for oxygen-rich blood to pass from the left ventricle into the aorta, where it is delivered to the rest of the body.
Blood flow through the heart
The "left" side of the heart controls the flow of oxygen-rich blood from the lungs to the entire body. The "right" side of the heart controls the flow of oxygen-poor blood from the veins in the body to the lungs.
Blood flows from the right and left atria into the ventricles through the open tricuspid and mitral valves, respectively; when the ventricles are full, the mitral and tricuspid valves close. This prevents blood from flowing backward into the atria while the ventricles contract.
As the ventricles begin to contract, the pulmonic and aortic valves are forced open and blood is pumped out of the ventricles through the open valves into the pulmonary artery toward the lungs, and into the aorta, to the body.
When the ventricles finish contracting and begin to relax, the aortic and pulmonic valves close. These valves prevent blood from flowing back into the ventricles. This cycle is repeated over and over, causing blood to flow continuously to the heart, lungs and body.
